Simulated Response of Electrochemical Sensors for Monitoring Molten-Salt Fueled Reactors

STUDENT PAPER: Advanced reactor concepts featuring molten salts as either the primary coolant or the actual fuel are gaining increased interest from the U.S. Department of Energy and the nuclear power industry. Examples include the Advanced High Temperature Reactor from Oak Ridge National Laboratory, the Waste Annihilation Molten Salt Reactor from MIT, and the Accelerator Driven Sub-Critical Molten Salt reactor from Texas A&M. These advanced nuclear reactor concepts are anticipated to be deployed in the future within and outside the United States, potentially including non-nuclear weapon states. Traditional international safeguards approaches rely heavily upon material accountancy, but that may be insufficient for these systems due to the quantities or concentrations of transuranic (TRU) elements in the fuel salt. Continuous and unattended process monitoring should be an effective supplemental safeguards measure in this case to complement material accountancy. This approach, however, requires robust sensors that are sufficiently sensitive to actinide concentrations in the fuel salt. Voltammetric methods that utilize a simple three-electrode probe have widely been studied for this applicationincluding cyclic, square wave, and normal pulse voltammetry. Based on the measured electrode potentials and peak heights, these methods can generally be correlated to concentrations of actinides and other ions in the salts. Some limitations to these methods may stem from the multi-component nature of these fuel salts. Most voltammetry studies published have focused on single actinides in a matrix salt. Even in single component studies, quantitative signal responses were found to be limited to a low range of concentrations. To provide the fundamental basis for development of advanced voltammetry systems that avoid or minimize these issues, a model called Enhanced REFIN with Anodic Dissolution (ERAD) was used to calculate voltage responses in molten LiCl-KCl with a range of UCl3 and ThCl4 concentrations. The model was developed based on first principles of mass transfer and electrochemistry. Based on ERAD simulations, the voltage response due to variations in hydrodynamic conditions and geometric configurations differs depending on the species present. Understanding the effect of these variations on voltage response is critical to developing electrochemical sensors and techniques for monitoring molten salt concentrations in advanced reactors.